Reactor coolant pump hydrostatic sealing assembly with improved hydraulic balance

摘要

A pump having a shaft and a housing containing pressurized fluid variable in pressure between pump startup and operation, employs a hydrostatic sealing assembly for sealably and rotatably mounting the shaft within the housing. The sealing assembly includes a runner mounted around the shaft for rotation therewith and a seal ring mounted to the stationary housing. The runner and seal ring have facing surfaces between which the pressurized fluid creates a flowing low pressure fluid film which prevents contact between the facing surfaces so long as a predetermined minimum leakrate is maintained therebetween. The seal ring has first and second surfaces facing in a direction opposite to that of its facing surface and in sealingly isolated relationship from one another. The first surface communicates with the pressurized fluid at supply pressure. A flow control device provided in the seal ring is automatically operable in response to the supply pressure level to open communication of the pressurized fluid supply pressure with the seal ring second surface at pump operation and to open communication of the fluid film low pressure with the seal ring second surface at pump startup. A lifting force thus imposed on the seal ring facing surface by the pressurized fluid is effectively balanced by a seating force imposed on the seal ring first and second surfaces at both pump startup and operation so that leakrates are produced between the facing surfaces during both pump startup and operation which are above the predetermined minimum.